As an example of a semiconductor device, there is known a NAND-type flash memory device having a 3D structure. In the manufacture of the NAND-type flash memory device having a 3D structure, a multilayer film, which is formed by stacking two layers having different dielectric constant alternately, is etched to form a deep hole in the multilayer film. Such etching is disclosed in U.S. Patent Application Publication No. 2013/0059450.
Specifically, referring to U.S. Patent Application publication No. 2013/0059450, the multilayer film is etched by exposing a target object having an amorphous carbon mask on the multilayer film to a plasma of a processing gas including CH2F2 gas, N2 gas and NF3 gas. Further, U.S. Patent Application Publication No. 2013/0059450 discloses a method for ramping down a pressure in a chamber during etching.
In the case of forming a deep hole in an etching target film by etching the multilayer film described above, the shape of the mask needs to be maintained until the etching is completed. In other words, a mask selectivity is required. However, the shape of the mask may not be maintained against the plasma of the processing gas disclosed in U.S. Patent Application Publication No. 2013/0059450.